Some of the conventional video cameras and still cameras have installed therein a camera-shake correcting function to correct a camera shake caused by a tremble of the camera user's hand holding the camera during shooting. Normally, the camera shake is corrected by image processing with the use of a CCD (charge-coupled device) imaging device or by optically correcting the optical axis displaced due to the camera shake.
It is proposed in the Japanese Patent Application No. 143330 of 1985 to detect an angular velocity applied to a camera by a small, inexpensive vibration gyro sensor, calculating an angular displacement from the detected angular velocity and controlling horizontal and vertical transfer of the CCD imaging device on the basis of the calculated angular displacement or moving a reflecting mirror to correct the optical axis or remove image blur caused by a vibration applied to the camera.
It is said that the optical correction of the optical axis displaced due to a camera shake is capable of a higher-quality imaging than the correction of the camera shake by image processing with the use of a CCD (charge-coupled device) imaging device because it can assure a blur-free image of an object. The optical axis displacement can be optically corrected by a so-called “shift lens system” in which part of an optical imaging lens is shifted in two directions perpendicular to the optical axis of an image pickup lens to shift the optical axis in order to move an image or by a “variable (apex) angle prism (VAP) system” using a VAP which shifts the optical axis by changing the apex angle.
The U.S. Pat. No. 3,212,420 discloses an example of the VAP system in which two transparent plates of a liquid-filled VAP, having a liquid filled between them, are tilted to change the apex angle of the prism for correcting the optical axis. Also, there is also known a VAP system in which a concave lens and convex lens having negative and positive curvatures, respectively, which are generally equal in magnitude to each other, and which are coupled with each other with their curved surfaces being opposite to each other (this lens combination is generally known as “Boskovice wedge”) are rotated about the center of their curvature to change the apex angle. The Japanese Examined Patent Application No. 5987 of 1969 discloses an example of the latter VAP system.
Also, the Japanese Patent Application Laid Open No. 294987 of 1995 proposes a concrete controlling method for shake correction in which a liquid-filled VAP is adopted as a shake-correcting optical system.
In the shift lens system, a group of lenses designed relatively small and lightweight may be used as a shift lens. In the VAP system, especially, the VAP system in which a liquid-filled VAP is used, there will occur a viscous resistance because the apex angle is changed by moving the liquid between glass sheets of the liquid-filled VAP. However, there will not take place any such viscous resistance in the shift lens system. Thus, the shift lens system is advantageous in that the entire apparatus can be designed small and a shake having high frequency components can easily be corrected.
In the shift lens system, however, since an image is moved by decentering the lens, an aberration will take place due to the lens decentering. Therefore, to prevent an image being deteriorated in quality due to such lens decentering, it is necessary to limit the image moving range, that is, the shake-correctable range.
On the other hand, in the shake correction by the VAP, bending the optical axis by the prism will cause chromatic aberration but it is said that the optical axis can be bent more largely than in the shift lens system.
Note however that the liquid-filled VAP has to be driven with a force overcoming the viscous resistance of the liquid for changing the apex angle and this VAP system is likely to be influenced by an environmental change such as pressure change.
In the VAP as a combination of concave and convex lenses, the radius of rotation of the lens is large, which will lead to a larger size of the entire apparatus, and thus, the VAP has not become popular. However, the Japanese Patent Application Laid Open No. 39358 of 1998 proposes to avoid any larger size of the entire apparatus by using a VAP that has a mechanism to rotate the combined concave and convex lenses while supporting each of the lenses at either end thereof in order to change the apex angle.
As above, there are proposed and used various optical shake-correcting techniques in practice. However, because of their differences in optical system from each other, they cannot be said to be advantageous in all cases. Therefore, it is desirable for the user of the camera that such optical shake-correcting techniques can selectively be adopted depending upon his or her intended imaging or exposure conditions.
The above requirement can be met by providing a camera body incorporating a lens-interchangeable camera system. In the optical shake-correcting system, the function of shake correction is provided on each interchangeable lens having an optical imaging system. Therefore, the camera body can use various optical shake-correcting systems by selecting an interchangeable lens depending upon intended exposure conditions.
Generally, correction of a camera shake needs at least a sensor to detect the camera shake, a calculation-controlling system to calculate a signal which activates a correcting optical system on the basis of the detected camera shake, and a driving system to actually operate the correcting optical system on the basis of the signal.
The correcting optical system is installed on an interchangeable lens, and so the driving system should be installed in the interchangeable lens. Also, the sensor and calculation-controlling system can be installed in the interchangeable lens, but since the correction-controlling system is changed from one to another each time the interchangeable lens is replaced, no constant operability of the camera body will not be assured through operations of shake correction.
If the sensor is left in the interchangeable lens while the calculation-controlling system is installed in the camera body in order to assure such a constant operability of the camera body, a signal from the sensor in the interchangeable lens is passed to the calculation-controlling system on the camera body and then sent to the driving system in the interchangeable lens. Thus, the signal communication will be complicated, and an interface will be required for the signal communication, resulting in an extremely inefficient camera system.
Therefore, the camera system should desirably have a configuration in which the sensor and calculation-controlling system are installed in the camera body and the driving system to drive the correcting optical system is installed in the interchangeable lens. Thus, there will be described below various camera systems in which the sensor and calculation-controlling system are installed in the camera body and the driving system to drive the correcting optical system is installed in the interchangeable lens.
The Japanese Patent Application Laid Open No. 105971 of 1997 proposes a camera system in which a shift lens system is adopted as a correcting optical system and a shift of a shift lens is calculated in a camera body and sent to an interchangeable lens.
Also, the Japanese Patent Application Laid Open No. 66445 of 1993 proposes a camera system in which a drive signal to drive a correcting optical system is calculated by a camera body from an angular velocity signal detected by the sensor and sent to an interchangeable lens.
Also, the Japanese Patent Application Laid Open No. 80511 of 1997 proposes a camera system in which an angular displacement signal detected by a sensor in a camera body is sent as a digital signal to an interchangeable lens.
Also, the Japanese Patent Application Laid Open No. 250272 of 1994 proposes a camera system in which a shift lens system is adopted as a correcting optical system.
Also, the Japanese Patent Application Laid Open No. 186435 of 1998 proposes a camera system in which a VAP as a combination of concave and convex lenses, as disclosed in the Japanese Patent Application Laid Open No. 39358 of 1998, is adopted as a correcting optical system and a control method of removing an error component caused when the apex angle of the VAP is changed is adopted.
As above, there has been proposed a plurality of correcting techniques in correcting optical systems different from each other for the purpose of optical shake correction. Naturally, the control methods for the shake correction are different from each other because they depend upon the correcting systems adopted therein. Therefore, even in a camera system designed to use a correcting optical system for each of interchangeable lenses so that the camera body can be used with every shake-correcting function, it should include a correcting system for each of the correcting systems.
In the camera systems each with the optical shake-correcting function, proposed in the Japanese Patent Application Laid Open Nos. 105971 of 1997, 66445 of 1993, 80511 of 1997, 250272 of 1994 and 186435 of 1998, respectively, the interchangeable lenses are used but the correcting optical system is exclusive to either the shift lens system or the VAP system. Namely, the camera system is low in versatility and the user of the camera system cannot select the advantages of the above-mentioned correcting optical systems. Therefore, the camera system will not be able to accommodate any correcting optical system based on a new principle at all.